Maxim MAX1760HEUB 0.8a, low-noise, 1mhz, step-up dc-dc converter Datasheet

19-1660; Rev 3; 1/07
KIT
ATION
EVALU
LE
B
A
IL
A
AV
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
The MAX1760/MAX1760H are high-efficiency, low-noise,
step-up DC-DC converters intended for use in batterypowered wireless applications. They combine low quiescent supply current (100µA) with a high 1MHz operating
frequency. Small external components and tiny 10-pin
TDFN and µMAX® packages make this device an excellent choice for small hand-held applications. The
MAX1760 is activated by a logic-low ON signal while the
MAX1760H is activated by a logic-high ON input.
Both devices use a synchronous-rectified pulse-widthmodulation (PWM) boost topology to generate 2.5V to
5.5V outputs from a wide range of inputs, such as 1 to 3
alkaline or NiCd/NiMH cells or a single lithium-ion (Li+)
cell. Proprietary Idle-Mode™ circuitry significantly
improves light-load efficiency and smoothly transitions to
fixed-frequency PWM operation at higher load currents.
Low-noise, forced-PWM mode is available for applications requiring constant-frequency operation at all load
currents. PWM operation can also be synchronized to
an external clock to protect sensitive frequency bands
in communications equipment. Analog soft-start and
adjustable current limit permit optimization of efficiency,
external component size, and output voltage ripple.
Applications
Features
♦ Up to 94% Efficiency
♦ 0.7V to 5.5V Input Range
♦ Up to 800mA Output
♦
♦
♦
♦
♦
Fixed 3.3V Output (or Adjustable from 2.5V to 5.5V)
PWM Synchronous-Rectified Topology
Low-Noise, Constant-Frequency Operation (1MHz)
0.1µA Logic-Controlled Shutdown
Synchronizable Switching Frequency
♦
♦
♦
♦
Adjustable Current Limit
Adjustable Soft-Start
10-Pin µMAX Package
10-Pin 3mm x 3mm TDFN Package
Ordering Information
PART
PINPACKAGE
ON
LOGIC
PKG CODE
T1033-1
MAX1760ETB
10 TDFN-EP*
Low
MAX1760EUB
10 µMAX
Low
U10-2
MAX1760HETB
10 TDFN-EP*
High
T1033-1
MAX1760HEUB
10 µMAX
High
U10-2
Digital Cordless Phones
PCS Phones
Wireless Handsets
Handheld Instruments
Palmtop Computers
Personal Communicators
Note: All devices are specified over the -40°C to +85°C operating
temperature range.
Typical Operating Circuit
Pin Configurations
*EP = Exposed paddle.
Two-Way Pagers
INPUT = 0.7V
TO VOUT
TOP VIEW
MAX1760
ON
CLK/SEL
POUT
VOUT = 3.3V,
800mA
ISET
REF
FB
10 ON (ON)
ISET 1
LX
ISET
1
9
POUT
REF
2
8
LX
GND
3
4
7
PGND
FB
5
6
CLK/SEL
OUT
REF
2
GND
3
FB
OUT
MAX1760
MAX1760H
10
ON (ON)
9
POUT
8
LX
4
7
PGND
5
6
CLK/SEL
MAX1760
MAX1760H
OUT
GND
PGND
µMAX
TDFN
(3mm x 3mm)
(ON) FOR MAX1760H
µMAX is a registered trademark of Maxim Integrated Products, Inc.
Idle Mode is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX1760/MAX1760H
General Description
MAX1760/MAX1760H
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
ABSOLUTE MAXIMUM RATINGS
ON, ON, OUT, CLK/SEL to GND ..................................-0.3V to +6V
PGND to GND ..........................................................................±0.3V
LX to PGND .................................................-0.3V to (VPOUT + 0.3V)
POUT to OUT ...........................................................................±0.3V
REF, FB, ISET, POUT to GND.......................-0.3V to (VOUT + 0.3V)
Continuous Power Dissipation (TA = +70°C)
Single-Layer Board:
10-Pin µMAX
(derate 5.6mW/°C above +70°C).................................….444mW
10-Pin TDFN-EP (derate 18.5mW/°C above +70°C) .....1482mW
Multilayer Board:
10-Pin µMAX (derate 8.8mW/°C above +70°C) ..........….707mW
10-Pin TDFN-EP (derate 24.4mW/°C above +70°C) .....1951mW
Operating Temperature Range................................-40°C to +85°C
Junction Temperature ...........................................................+150°C
Storage Temperature Range .................................-65°C to +150°C
Lead Temperature (soldering, 10s)......................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(CLK/SEL = FB = PGND = GND, ISET = REF, OUT = POUT, VOUT = 3.6V, TA = 0°C to +85°C. Typical values are at TA = +25°C,
unless otherwise noted.)
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
DC-DC CONVERTER
Input Voltage Range
(Note 1)
0.7
5.5
Minimum Startup Voltage
ILOAD < 1mA, TA = +25°C (Note 2)
0.9
1.1
Temperature Coefficient of Startup Voltage
ILOAD < 1mA
-2.3
Frequency in Startup Mode
VOUT = 1.5V
125
500
1000
kHz
Internal Oscillator Frequency
CLK/SEL = OUT
0.8
1
1.2
MHz
Oscillator Maximum Duty Cycle
(Note 3)
80
86
External Clock Frequency Range
0.5
V
mV/°C
90
%
1.2
MHz
Output Voltage
VFB < 0.1V, CLK/SEL = OUT, includes load
regulation for 0 < ILX < 0.55A
3.17
3.3
3.38
V
FB Regulation Voltage
Adjustable output, CLK/SEL = OUT, includes
load regulation for 0 < ILX < 0.55A
1.215
1.240
1.270
V
FB Input Leakage Current
VFB = 1.35V (TA = +25°C, MAX1760ETB,
MAX1760HETB)
0.01
100
nA
Load Regulation
CLK/SEL = OUT, no load to full load
(0 < ILX < 1.0A)
-1.5
Output Voltage Adjust Range
2.5
%
5.5
V
2.15
2.30
V
±0.01
±50
nA
V ON = 3.6V, VON = 0V
0.1
5
µA
No-Load Supply Current
CLK/SEL = GND (Note 5)
100
185
No-Load Supply Current Forced-PWM Mode
CLK/SEL = OUT
2.5
POUT Leakage Current
VLX = 0, VOUT = 5.5V (TA = +25°C,
MAX1760ETB, MAX1760HETB)
0.1
10
µA
LX Leakage Current
VLX = VOUT = 5.5V, in shutdown (TA =
+25°C, MAX1760ETB, MAX1760HETB)
0.1
10
µA
Output Voltage Lockout Threshold
Rising edge (Note 4)
ISET Input Leakage Current
VISET = 1.25V (TA = +25°C, MAX1760ETB,
MAX1760HETB)
Supply Current in Shutdown
2.00
µA
mA
DC-DC SWITCHES
2
_______________________________________________________________________________________
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
(CLK/SEL = FB = PGND = GND, ISET = REF, OUT = POUT, VOUT = 3.6V, TA = 0°C to +85°C. Typical values are at TA = +25°C,
unless otherwise noted.)
PARAMETER
Switch On-Resistance
TYP
MAX
N-channel
CONDITIONS
0.15
0.28
P-channel
0.25
0.45
N-Channel Current Limit
P-Channel Turn-Off Current
CLK/SEL = GND
MIN
UNITS
Ω
1.0
1.25
1.6
A
20
60
120
mA
1.230
1.250
1.270
V
5
15
mV
0.2
5
mV
0.2 x
VOUT
V
REFERENCES
Reference Output Voltage
IREF = 0
Reference Load Regulation
-1µA < IREF < +50µA
Reference Supply Rejection
2.5V < VOUT < 5V
LOGIC INPUTS
CLK/SEL Input Low Level
2.5V ≤ VOUT ≤ 5.5V
CLK/SEL Input High Level
2.5V ≤ VOUT ≤ 5.5V
ON, ON Input Low Level (Note 6)
ON, ON Input High Level (Note 6)
Input Leakage Current
0.8 x
VOUT
V
1.1V ≤ VOUT ≤ 1.8V
0.2
1.8V ≤ VOUT ≤ 5.5V
0.4
1.1V ≤ VOUT ≤ 1.8V
VOUT
- 0.2
1.8V ≤ VOUT ≤ 5.5V
1.6
CLK/SEL, ON, ON (TA = +25°C,
MAX1760ETB, MAX1760HETB)
V
V
0.01
1
µA
Minimum CLK/SEL Pulse Width
200
ns
Maximum CLK/SEL Rise/Fall Time
100
ns
ELECTRICAL CHARACTERISTICS
(CLK/SEL = FB = PGND = GND, ISET = REF, OUT = POUT, VOUT = 3.6V, TA = -40°C to +85°C, unless otherwise noted.) (Note 7)
PARAMETER
CONDITIONS
MIN
MAX
UNITS
DC-DC CONVERTER
Output Voltage
VFB < 0.1V, CLK/SEL = OUT, includes load
regulation for 0 < ILX < 0.55A
3.17
3.38
V
FB Regulation Voltage
Adjustable output, CLK/SEL = OUT, includes
load regulation for 0 < ILX < 0.55A
1.215
1.270
V
Internal Oscillator Frequency
CLK/SEL = OUT
0.75
1.2
MHz
80
90
%
2.00
2.30
V
5
µA
µA
Oscillator Maximum Duty Cycle
(Note 3)
Output Voltage Lockout Threshold
Rising edge (Note 4)
Supply Current in Shutdown
V ON = 3.6V
No-Load Supply Current
CLK/SEL = GND (Note 5)
185
N-channel
0.28
P-channel
0.45
DC-DC SWITCHES
Switch On-Resistance
Ω
_______________________________________________________________________________________
3
MAX1760/MAX1760H
ELECTRICAL CHARACTERISTICS (continued)
ELECTRICAL CHARACTERISTICS (continued)
(CLK/SEL = FB = PGND = GND, ISET = REF, OUT = POUT, VOUT = 3.6V, TA = -40°C to +85°C, unless otherwise noted.) (Note 7)
PARAMETER
CONDITIONS
N-Channel Current Limit
MIN
MAX
UNITS
1.0
1.6
A
1.230
1.270
V
0.2 x
VOUT
V
REFERENCE
Reference Output Voltage
IREF = 0
LOGIC INPUTS
CLK/SEL Input Low Level
2.5V ≤ VOUT ≤ 5.5V
CLK/SEL Input High Level
2.5V ≤ VOUT ≤ 5.5V
ON, ON Input Low Level (Note 6)
0.8 x
VOUT
V
1.1V ≤ VOUT ≤ 1.8V
0.2
1.8V ≤ VOUT ≤ 5.5V
0.4
1.1V ≤ VOUT ≤ 1.8V
ON, ON Input High Level (Note 6)
V
VOUT + 0.2
1.8V ≤ VOUT ≤ 5.5V
V
1.6
CLK/SEL, ON, ON
Input Leakage Current
1
µA
Note 1: Operating voltage—since the regulator is bootstrapped to the output, once started, the MAX1760 operates down
to 0.7V input.
Note 2: Startup is tested with the circuit shown in Figure 6.
Note 3: Defines maximum step-up ratio.
Note 4: The regulator is in startup mode until this voltage is reached. Do not apply full load current until the output exceeds 2.3V.
Note 5: Supply current into the OUT pin. This current correlates directly to the actual battery-supply current, but is reduced in
value according to the step-up ratio and efficiency.
Note 6: ON (MAX1760) and ON (MAX1760H) have a hysteresis of approximately 0.15 × VOUT.
Note 7: Specifications to -40°C are guaranteed by design and not production tested.
Typical Operating Characteristics
(Circuit of Figure 2, VIN = 2.4V, VOUT = 3.3V, TA = +25°C, unless otherwise noted.)
70
60
C
50
40
= AUTO MODE
= FPWM MODE
A: VIN = 2.4V
B: VIN = 1.2V
C: VIN = 0.9V
30
20
10
0
0.0001
0.001
0.01
0.1
OUTPUT CURRENT (A)
4
EFFICIENCY (%)
B
B
80
80
70
60
50
40
= AUTO MODE
= FPWM MODE
A: VIN = 3.6V
B: VIN = 2.4V
C: VIN = 1.2V
20
10
1
A
C
30
0
0.0001
0.9
MAX1760-03
90
0.8
OUTPUT CURRENT (A)
A
90
MAX1760-02
100
MAX1760 toc01
100
MAXIMUM OUTPUT CURRENT
vs. INPUT VOLTAGE
EFFICIENCY vs. OUTPUT CURRENT
VOUT = 5V
EFFICIENCY vs. OUTPUT CURRENT
VOUT = 3.3V
EFFICIENCY (%)
MAX1760/MAX1760H
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
VOUT = 3.3V
0.7
0.6
VOUT = 5V
0.5
0.4
0.3
0.2
0.1
0.001
0.01
0.1
OUTPUT CURRENT (A)
1
0.5
1.0
1.5 2.0 2.5 3.0
INPUT VOLTAGE (V)
_______________________________________________________________________________________
3.5
4.0
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
NO-LOAD BATTERY CURRENT
vs. INPUT VOLTAGE
TOTAL SHUTDOWN CURRENT
(ILX + IOUT) vs. INPUT VOLTAGE
1.5
1.0
VOUT = 5V
0.5
0.1
3
4
0
5
STARTUP VOLTAGE
vs. OUTPUT CURRENT
1
PEAK INDUCTOR CURRENT (A)
C
1.5
1.0
0.5
3
4
5
0.75
6
-40
0.01
10
35
60
85
TEMPERATURE (°C)
PEAK INDUCTOR CURRENT vs. VISET
HEAVY-LOAD SWITCHING WAVEFORMS
MAX1760-08
1.2
A
1.0
0.8
B
0.6
0.4
C
0.2
CIRCUIT OF FIGURE 6
-15
INPUT VOLTAGE (V)
1.4
MAX1760-07
2.0
2
0V
0.0
0.1
1
0.1
0.3
0.5
0.7
0.9
1.1
VISET (V)
LIGHT-LOAD SWITCHING WAVEFORMS
LOAD-TRANSIENT RESPONSE
A
1.3
A = LX PIN, 5V/div
B = INDUCTOR CURRENT, 200mA/div
C = OUTPUT RIPPLE, 50mV/div AC-COUPLED
t = 400ns/div
LINE-TRANSIENT RESPONSE
MAX1760-11
OUTPUT CURRENT (A)
MAX1760-10
STARTUP VOLTAGE (V)
A = +85°C
B = +25°C
C = -40°C
0.0
0.001
0.90
MAX1760-09
2
B
0.95
MAX1760-12
1
A
1.00
0.85
INPUT VOLTAGE (V)
2.5
MAX1760-06
MAX1760-05
1
1.05
0.80
0.0
3.0
1.15
1.10
VOUT = 3.3V
0
1.20
FREQUENCY (MHz)
SHUTDOWN CURRENT (nA)
2.0
INPUT CURRENT (mA)
10
MAX1760-04
2.5
INTERNAL OSCILLATOR
FREQUENCY vs. TEMPERATURE
A
A
B
B
B
C
t = 400ns/div
A = LX PIN, 5V/div
B = INDUCTOR CURRENT, 200mA/div
C = OUTPUT RIPPLE, 50mV/div, AC-COUPLED
t = 200ms/div
VIN = 1.1V, VOUT = 3.3V, IOUT = 0 AND 0.2A
A = IOUT, 100mA/div
B = VOUT, 50mV/div, AC-COUPLED
400µs/div
VIN = 2.4V TO 1.4V, IOUT = 70mA
A = VIN, 1V/div
B = VOUT, 5mA/div, AC-COUPLED
_______________________________________________________________________________________
5
MAX1760/MAX1760H
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VIN = 2.4V, VOUT = 3.3V, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(Circuit of Figure 2, VIN = 2.4V, VOUT = 3.3V, TA = +25°C, unless otherwise noted.)
TURN-ON WAVEFORMS
NO SOFT-START COMPONENTS
12
A
MAX1760-15
MAX1760-13
16
SOFT-START WAVEFORMS
RSS = 500kΩ, CSS = 0.1µF
MAX1760-14
NOISE SPECTRUM
NOISE (mVRMS)
MAX1760/MAX1760H
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
A
8
B
B
4
C
0
C
0V
OV
0.1
1
10
FREQUENCY (MHz)
t = 2ms/div
2.00ms/div
A = ON, 5V/div
B = INPUT CURRENT, 500mA/div
C = VOUT, 2V/div
A = ON, 5V/div
B = INPUT CURRENT, 100mA/div
C = VOUT, 2V/div
Pin Description
NAME
FUNCTION
1
ISET
N-Channel Current-Limit Control. For maximum current limit, connect to REF. To reduce current, supply a
voltage between REF and GND by means of a resistive voltage-divider. If soft-start is desired, connect a
capacitor from ISET to GND. When ON = high, or VREF <80% of nominal value, an on-chip 100kΩ switched
resistor discharges this pin to GND.
2
REF
1.250V Voltage Reference Bypass. Connect a 0.22µF ceramic bypass capacitor to GND. Up to 50µA of
external load current is allowed.
3
GND
Ground. Connect to PGND with short trace.
4
FB
5
OUT
PIN
6
CLK/SEL
7
PGND
8
LX
9
POUT
10
—
6
DC-DC Converter Feedback Input. To set fixed output voltage of +3.3V, connect FB to ground. For
adjustable output of 2.5V to 5.5V, connect to a resistive divider from OUT to GND. FB set point = 1.24V.
IC Power, Supplied from the Output. Bypass to GND with a 0.68µF ceramic capacitor, and connect to POUT
with a series 4.7Ω resistor (Figure 2).
Clock Input for the DC-DC Converter. Also serves to program operating mode of switcher as follows:
CLK/SEL = LO: Normal operation—operates at a fixed frequency, automatically switching to low-power
mode if load is minimized.
CLK/SEL = HI: Forced-PWM mode—operates in low-noise, constant-frequency mode at all loads.
CLK/SEL = Clocked: Forced-PWM mode with the internal oscillator synchronized to CLK in 500kHz to
1200kHz range.
Source of N-Channel Power MOSFET Switch
Inductor Connection
Power Output. P-channel synchronous-rectifier source.
ON
MAX1760 Enable Input. When ON is low, the IC is on. Connect to GND for normal operation.
ON
MAX1760H Enable Input. When ON is high, the IC is on. Connect to OUT for normal operation.
EP
Exposed Paddle (TDFN Package Only). Internally connected to GND. Connect to a large ground plane to
maximize thermal dissipation. Do not use as sole ground connection.
_______________________________________________________________________________________
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
MAX1760/MAX1760H
UNDERVOLTAGE LOCKOUT
OUT
IC POWER
CONTROLLER
POUT
2.15V
STARTUP
OSCILLATOR
EN
ON
(MAX1760H)
ON
(MAX1760)
ON
1.25V
REF
GND
GND
PCH
D
LX
RDY
REFERENCE
REF
Q
EN
EN
OSC
OSC
NCH
OSCILLATOR
1MHz
CLK/SEL
MODE
MODE
PGND
CLK/SEL
FB
FB
ISET
ISET
MAX1760
Figure 1. Functional Diagram
Detailed Description
The MAX1760 is a highly efficient, low-noise power supply for portable RF and hand-held instruments. It combines a boost switching regulator, N-channel power
MOSFET, P-channel synchronous rectifier, precision
reference, and shutdown control (Figure 1).
The DC-DC converter boosts a 1-cell to 3-cell battery
voltage input to a fixed 3.3V or adjustable voltage
between 2.5V and 5.5V. An external Schottky diode is
required for output voltages greater than 4V. The
MAX1760 guarantees startup with an input voltage as
low as 1.1V and remains operational down to an input
of just 0.7V. It is optimized for use in cellular phones
and other applications requiring low noise and low quiescent current for maximum battery life. It features
fixed-frequency operation at medium and heavy loads,
but at light loads, switches only as needed for optimum
efficiency. This device is also capable of constant-frequency (1MHz), low-noise PWM operation at all load
currents, or frequency-synchronized PWM operation
when connected to an external clock. Table 1 lists
some typical outputs. Shutdown reduces quiescent current to just 1µA. Figure 2 shows the standard application circuit for the MAX1760.
3.3µH
VIN = 2.4V
33µF
ON
LX
CLK/SEL
MAX1760
ISET
REF
0.22µF
FB
V OUT = 3.3V,
800mA
POUT
4.7Ω
100µF
OUT
GND PGND
0.68µF
Figure 2. Standard Application Circuit
Step-Up Converter
During DC-DC converter operation, the internal N-channel MOSFET switch turns on for the first part of each
cycle, allowing current to ramp up in the inductor and
store energy in a magnetic field. During the second
part of each cycle, the MOSFET turns off and inductor
current flows through the synchronous rectifier to the
_______________________________________________________________________________________
7
MAX1760/MAX1760H
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
Table 1. Typical Available Output Current
NUMBER OF NiCd/NiMH
CELLS
INPUT VOLTAGE
(V)
OUTPUT VOLTAGE
(V)
OUTPUT CURRENT
(mA)
1
1.2
3.3
350
2.4
3.3
800
2.4
5.0
500
3.6
5.0
750
2
3
Table 2. Selecting the Operating Mode
CLK/SEL
MODE
FEATURES
0
Normal operation
1
Forced PWM
Low noise, fixed frequency at all loads.
External clock
500kHz to 1.2MHz
Synchronized PWM
Low noise, fixed frequency at all loads.
High efficiency at all loads. Fixed frequency at all but light loads.
output filter capacitor and the load. As the energy
stored in the inductor is depleted, the current ramps
down and the synchronous rectifier turns off. At light
loads, the device operates at fixed frequency or only as
needed to maintain regulation, depending on the
CLK/SEL setting (Table 2).
Normal Operation
Pulling CLK/SEL low selects the MAX1760’s normal
operating mode. In this mode, the device operates in
PWM when driving medium-to-heavy loads, and automatically switches to PFM if the load requires less
power. PFM operation allows higher efficiency than
PWM under light-load conditions.
Forced-PWM Operation
When CLK/SEL is high, the MAX1760 operates in a lownoise PWM-only mode. During forced-PWM operation,
the MAX1760 switches at a constant frequency (1MHz)
and modulates the MOSFET switch pulse width to control the power transferred per cycle to regulate the output voltage. Switching harmonics generated by
fixed-frequency operation are consistent and easily filtered. See the Noise Spectrum plot in the Typical
Operating Characteristics.
Synchronous Rectifier
The MAX1760 features an internal, P-channel synchronous rectifier to enhance efficiency. Synchronous rectification provides 5% improved efficiency over similar
nonsynchronous boost regulators. In PWM mode, the
synchronous rectifier is turned on during the second
half of each switching cycle. In low-power mode, an
internal comparator turns on the synchronous rectifier
when the voltage at LX exceeds the boost regulator
output, and turns it off when the inductor current drops
below 60mA. When setting output voltages greater than
4V, an external 0.5A Schottky diode must be connected
in parallel with the on-chip synchronous rectifier.
Low-Voltage Startup Oscillator
The MAX1760 uses a CMOS, low-voltage startup oscillator for a 1.1V guaranteed minimum startup input voltage. At startup, the low-voltage oscillator switches the
N-channel MOSFET until the output voltage reaches
2.15V. Above this level, the normal boost-converter
feedback and control circuitry take over. Once the
device is in regulation, it can operate down to 0.7V
input since internal power for the IC is bootstrapped
from the output through OUT. Do not apply full load
until the output exceeds 2.3V.
Synchronized-PWM Operation
The MAX1760 can be synchronized in PWM mode to an
external frequency of 500kHz to 1.2MHz by applying an
external clock signal to CLK/SEL. This allows interference to be minimized in wireless applications. The synchronous rectifier is active during synchronized-PWM
operation.
8
Shutdown
The MAX1760 has a shutdown mode that reduces quiescent current to 0.1µA. During shutdown (ON = high
on MAX1760, ON = low on MAX1760H), the reference
and all feedback and control circuitry are off. During
shutdown, the output voltage is one diode drop below
the input voltage.
_______________________________________________________________________________________
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
MAX1760
3.3µH
VIN = 2.4V
33µF
CLK/SEL
LX
ON
MAX1760
ISET
REF
0.22µF
PGND GND
POUT
VOUT
100µF
4.7Ω
OUT
FB
0.68µF
R1
R1 = R2
R2
(
)
VOUT
-1
VFB
VFB = 1.24V
Figure 3. Connecting Resistors for External Feedback
REF
REF
0.22µF
RSS
ILIM = 1.25A
MAX1760
ILIM = 1.25A
0.22µF
RSS1
tSS = RSSCSS
MAX1760
(
RSS2
RSS1 + RSS2
)
tSS = (RSS1 II RSS2) CSS
ISET
ISET
RSS2
CSS
RSS ≥ 470kΩ
Figure 4. Soft-Start with Maximum Switch Limit Current
Reference
The MAX1760 has an internal 1.250V ±1% reference.
Connect a 0.22µF ceramic bypass capacitor from REF
to GND within 0.2in (5mm) of the REF pin. REF can
source up to 50µA of external load current.
Design Procedure
Setting the Output Voltages
For a fixed 3.3V output, connect FB to GND. To set
other output voltages between 2.5V and 5.5V, connect
a resistor voltage-divider to FB from OUT to GND
(Figure 3). The input bias current into FB is <20nA,
allowing large-value divider resistors without sacrificing
accuracy. Connect the resistor voltage-divider as close
to the IC as possible, within 0.2in (5mm) of FB. Choose
R2 of 270kΩ or less, then calculate R1 using:
V

R1 = R2  OUT − 1
 VFB

CSS
RSS1 ≥ 470kΩ
Figure 5. Soft-Start with Reduced Switch Current Limit
where VFB, the boost-regulator feedback set point, is
1.24V.
Setting the Switch Current Limit
and Soft-Start
The ISET pin adjusts the inductor current limit and
implements soft-start. With ISET connected to REF, the
inductor current limits at 1.25A. With ISET connected to
a resistive divider set from REF to GND, the current limit
is reduced according to:
V

ILIM = 1.25A  ISET 
 1.25V 
Implement soft-start by placing a resistor from ISET to
REF and a capacitor from ISET to GND. In shutdown,
ISET is discharged to GND through an on-chip 100kΩ
resistor. At power-up, ISET is 0V and the LX current is
zero. As the capacitor voltage rises, the current
increases and the output voltage rises. The soft-start
_______________________________________________________________________________________
9
MAX1760/MAX1760H
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
Table 3. Component Selection Guide
PRODUCTION METHOD
INDUCTORS
CAPACITORS
DIODES
TOKO type D52LC
AVX TPS series
EIC SB series
TOKO type D518LC
Kemet T510 series
Motorola MBR0520L
Sumida CDRH5D18
Sanyo POSCAP series
—
Sumida CDRH4D28
—
—
Surface mount
Table 4. Component Suppliers
SUPPLIER
PHONE
AVX
USA: 843-448-9411
EIC
USA: 916-941-0712
Kemet
USA: 810-287-2536
Motorola
USA: 408-629-4789
Japan: 81-45-474-7030
Sumida
USA: 847-956-0666
Japan: 011-81-3-3667-3302
TOKO
USA: 847-297-0070
Note: Please indicate that you are using the MAX1760 when
contacting these component suppliers.
External Diode
For output voltages greater than 4V, an external
Schottky diode must be connected from LX to POUT, in
parallel with the on-chip synchronous rectifier (Figure
6). The diode should be rated for 0.5A. Representative
devices are Motorola MBR0520L, Nihon EP05Q03L, or
generic 1N5817. This external diode is also recommended for applications that must start with input voltages at or below 1.8V. The Schottky diode carries
current during startup and after the synchronous rectifier turns off; thus, its current rating only needs to be
500mA. Connect the diode as close to the IC as possible. Do not use ordinary rectifier diodes; their slow
switching speeds and long reverse-recovery times render them unacceptable. For circuits that do not require
startup with inputs below 1.8V and have an output of 4V
or less, no external diode is needed.
time constant is:
Input and Output Filter Capacitors
t SS = RSS CSS
where RSS ≥ 470kΩ.
Placing a capacitor across the lower resistor of the current-limiting resistive divider provides both current-limit
and soft-start features simultaneously (Figures 4 and 5).
Choose input and output filter capacitors that will service the input and output peak currents with acceptable voltage ripple. Choose input capacitors with
working voltage ratings over the maximum input volt-
Inductor Selection
The MAX1760’s high switching frequency allows the
use of a small 3.3µH surface-mount inductor. The chosen inductor should generally have a saturation current
rating exceeding the N-channel switch current limit;
however, it is acceptable to bias the inductor current
into saturation by as much as 20% if a slight reduction
in efficiency is acceptable. Lower current-rated inductors may be used if ISET is employed to reduce the
peak inductor current (see the Setting the Switch
Current Limit and Soft-Start section). For high efficiency, choose an inductor with a high-frequency ferrite
core material to reduce core losses. To minimize radiated noise, use a toroid or shielded inductor. See Table 3
for suggested components and Table 4 for a list of
component suppliers. Connect the inductor from the
battery to the LX pin as close to the IC as possible.
10
3.3µH
VIN = 0.7V
TO VOUT
33µF
CLK/SEL
MRB0520L
MAX1760
100µF
POUT
ISET
REF
0.22µF
VOUT
LX
ON
PGND GND
4.7Ω
OUT
FB
0.68µF
Figure 6. Connection with External Schottky Diode for Output
Voltages Greater than 4V, or to Assist Low-Voltage Startup
______________________________________________________________________________________
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
The input filter capacitor reduces peak currents drawn
from the input source and also reduces input switching
noise. The input voltage source impedance determines
the required value of the input capacitor. When operating directly from one or two NiMH cells placed close to
the MAX1760, use a single 33µF low-ESR input filter
capacitor. With higher impedance batteries, such as
alkaline and Li+, a higher value input capacitor may
improve efficiency.
The output filter capacitor reduces output ripple voltage
and provides the load with transient peak currents
when necessary. For the output, a 100µF, low-equivalent-series-resistance (ESR) capacitor is recommended
for most applications.
Sanyo POSCAP, Panasonic SP/CB, and Kemet T510
are good low-ESR capacitors. Low-ESR tantalum
capacitors offer a good tradeoff between price and
performance. Do not exceed the ripple current ratings
of tantalum capacitors. Avoid aluminum electrolytic
capacitors; their high ESR typically results in higher
output ripple voltage.
Other External Components
Two ceramic bypass capacitors are required for proper
operation. Bypass REF to GND with 0.22µF. Also,
bypass OUT to GND with a 0.68µF ceramic capacitor,
and connect OUT to POUT with a 4.7Ω resistor. Each of
these components should be placed as close to its
respective IC pins as possible, within 0.2in (5mm).
Table 4 lists suggested suppliers.
Layout Considerations
High switching frequencies and large peak currents
make PCB layout a critical part of design. Poor design
causes excessive EMI and ground bounce, both of
which can cause instability or regulation errors by corrupting the voltage and current feedback signals.
Power components—such as the inductor, converter IC,
filter capacitors, and output diode—should be placed
as close together as possible, and their traces should
be kept short, direct, and wide. Keep the voltage feedback network very close to the IC, within 0.2in (5mm) of
the FB pin. Keep noisy traces, such as those from the
LX pin, away from the voltage feedback network and
guarded from them using grounded copper. Refer to the
MAX1760 evaluation kit for a full PCB example.
Chip Information
TRANSISTOR COUNT: 1361
______________________________________________________________________________________
11
MAX1760/MAX1760H
age, and output capacitors with working voltage ratings
higher than the output.
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
e
10LUMAX.EPS
MAX1760/MAX1760H
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
4X S
10
10
INCHES
H
Ø0.50±0.1
0.6±0.1
1
1
0.6±0.1
BOTTOM VIEW
TOP VIEW
D2
MILLIMETERS
MAX
DIM MIN
0.043
A
0.006
A1
0.002
A2
0.030
0.037
0.120
D1
0.116
0.118
D2
0.114
E1
0.116
0.120
0.118
E2
0.114
0.199
H
0.187
L
0.0157 0.0275
L1
0.037 REF
b
0.007
0.0106
e
0.0197 BSC
c
0.0035 0.0078
0.0196 REF
S
α
0°
6°
MAX
MIN
1.10
0.05
0.15
0.75
0.95
2.95
3.05
2.89
3.00
2.95
3.05
2.89
3.00
4.75
5.05
0.40
0.70
0.940 REF
0.177
0.270
0.500 BSC
0.090
0.200
0.498 REF
0°
6°
E2
GAGE PLANE
A2
c
A
b
A1
α
E1
D1
FRONT VIEW
L
L1
SIDE VIEW
PROPRIETARY INFORMATION
TITLE:
PACKAGE OUTLINE, 10L uMAX/uSOP
APPROVAL
DOCUMENT CONTROL NO.
21-0061
12
______________________________________________________________________________________
REV.
1
1
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
6, 8, &10L, DFN THIN.EPS
PACKAGE OUTLINE, 6,8,10 & 14L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
21-0137
H
1
2
______________________________________________________________________________________
13
MAX1760/MAX1760H
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
MAX1760/MAX1760H
0.8A, Low-Noise, 1MHz,
Step-Up DC-DC Converter
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
PACKAGE VARIATIONS
COMMON DIMENSIONS
SYMBOL
MIN.
MAX.
PKG. CODE
N
D2
E2
e
JEDEC SPEC
b
A
0.70
0.80
T633-1
6
1.50±0.10
2.30±0.10
0.95 BSC
MO229 / WEEA
0.40±0.05
1.90 REF
D
2.90
3.10
T633-2
6
1.50±0.10
2.30±0.10
0.95 BSC
MO229 / WEEA
0.40±0.05
1.90 REF
[(N/2)-1] x e
E
2.90
3.10
T833-1
8
1.50±0.10
2.30±0.10
0.65 BSC
MO229 / WEEC
0.30±0.05
1.95 REF
A1
0.00
0.05
T833-2
8
1.50±0.10
2.30±0.10
0.65 BSC
MO229 / WEEC
0.30±0.05
1.95 REF
L
0.20
0.40
1.95 REF
T833-3
8
1.50±0.10
2.30±0.10
0.65 BSC
MO229 / WEEC
0.30±0.05
k
0.25 MIN.
T1033-1
10
1.50±0.10
2.30±0.10
0.50 BSC
MO229 / WEED-3
0.25±0.05
2.00 REF
A2
0.20 REF.
T1033-2
10
1.50±0.10
2.30±0.10
0.50 BSC
MO229 / WEED-3
0.25±0.05
2.00 REF
T1433-1
14
1.70±0.10
2.30±0.10
0.40 BSC
----
0.20±0.05
2.40 REF
T1433-2
14
1.70±0.10
2.30±0.10
0.40 BSC
----
0.20±0.05
2.40 REF
PACKAGE OUTLINE, 6,8,10 & 14L,
TDFN, EXPOSED PAD, 3x3x0.80 mm
21-0137
-DRAWING NOT TO SCALE-
H
2
2
Revision History
Pages changed at Rev 3: 1, 2, 6, 11, 14
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2007 Maxim Integrated Products
is a registered trademark of Maxim Integrated Products, Inc.